text: // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file. See the AUTHORS file for names of contributors.
  //
  // Slice is a simple structure containing a pointer into some external
  // storage and a size.  The user of a Slice must ensure that the slice
  // is not used after the corresponding external storage has been
  // deallocated.
  //
  // Multiple threads can invoke const methods on a Slice without
  // external synchronization, but if any of the threads may call a
  // non-const method, all threads accessing the same Slice must use
  // external synchronization.
  
  #ifndef STORAGE_LEVELDB_INCLUDE_SLICE_H_
  #define STORAGE_LEVELDB_INCLUDE_SLICE_H_
  
  #include <assert.h>
  #include <stddef.h>
  #include <string.h>
  #include <string>
  
  namespace leveldb {
  
  class Slice {
   public:
    // Create an empty slice.
    Slice() : data_(""), size_(0) { }
  
    // Create a slice that refers to d[0,n-1].
    Slice(const char* d, size_t n) : data_(d), size_(n) { }
  
    // Create a slice that refers to the contents of "s"
    Slice(const std::string& s) : data_(s.data()), size_(s.size()) { }
  
    // Create a slice that refers to s[0,strlen(s)-1]
    Slice(const char* s) : data_(s), size_(strlen(s)) { }
  
    // Return a pointer to the beginning of the referenced data
    const char* data() const { return data_; }
  
    // Return the length (in bytes) of the referenced data
    size_t size() const { return size_; }
  
    // Return true iff the length of the referenced data is zero
    bool empty() const { return size_ == 0; }
  
    // Return the ith byte in the referenced data.
    // REQUIRES: n < size()
    char operator[](size_t n) const {
      assert(n < size());
      return data_[n];
    }
  
    Slice copy() {
      char * new_data = new char[size_];
      memcpy(new_data, data_, size_);
      return Slice(new_data, size_);
    }
  
    // Change this slice to refer to an empty array
    void clear() { data_ = ""; size_ = 0; }
  
    // Drop the first "n" bytes from this slice.
    void remove_prefix(size_t n) {
      assert(n <= size());
      data_ += n;
      size_ -= n;
    }
  
    // Return a string that contains the copy of the referenced data.
    std::string ToString() const { return std::string(data_, size_); }
  
    // Three-way comparison.  Returns value:
    //   <  0 iff "*this" <  "b",
    //   == 0 iff "*this" == "b",
    //   >  0 iff "*this" >  "b"
    int compare(const Slice& b) const;
  
    // Return true iff "x" is a prefix of "*this"
    bool starts_with(const Slice& x) const {
      return ((size_ >= x.size_) &&
              (memcmp(data_, x.data_, x.size_) == 0));
    }
  
   private:
    const char* data_;
    size_t size_;
  
    // Intentionally copyable
  };
  
  inline bool operator==(const Slice& x, const Slice& y) {
    return ((x.size() == y.size()) &&
            (memcmp(x.data(), y.data(), x.size()) == 0));
  }
  
  inline bool operator!=(const Slice& x, const Slice& y) {
    return !(x == y);
  }
  
  inline int Slice::compare(const Slice& b) const {
    const size_t min_len = (size_ < b.size_) ? size_ : b.size_;
    int r = memcmp(data_, b.data_, min_len);
    if (r == 0) {
      if (size_ < b.size_) r = -1;
      else if (size_ > b.size_) r = +1;
    }
    return r;
  }
  
  }  // namespace leveldb
  
  
  #endif  // STORAGE_LEVELDB_INCLUDE_SLICE_H_
  